Orthogonalized spatial multiplexing for wireless communication

ABSTRACT

A method and system for processing information data in a wireless communications system for reducing the complexity in spatial multiplexing of signals over different transmit antennas. In orthogonalized spatial multiplexing with the resolution of one, encoded data are interleaved and converted into a plurality of parallel sub-streams. Each sub-stream is then spreaded with a user specific spreading code with an intentional delay offset of few chips prior to modulating the encoded data for transmission. Likewise, in orthogonalized spatial multiplexing with the resolution of two, encoded data are interleaved and converted into a plurality of parallel sub-stream pairs. Each sub-stream pair is spreaded pairwise with a user specific spreading code with an intentional delay offset of few chips.

FILED OF THE INVENTION

[0001] The present invention relates generally to a spatial multiplexingsystem and, more particularly, to MIMO high speed downlink WCDMA FDD.

BACKGROUND OF THE INVENTION

[0002] The demand and growth of wireless communication services requiresreliable and fast transmission of data and video with data rates ofseveral Megabits per second. The fundamental phenomenon that makesreliable wireless transmission difficult is the time-varying multi-pathfading, with the rates depending on the mobility of the user. Sendingmultiple copies of the same transmitted signal through possiblyindependent fading channels increases the probability that at least oneof them will arrive at the receiver without being severely deteriorated.This technique is called diversity. It presents the single mostimportant and well-established solution for the reliable wirelesscommunication. Different diversity methods such as temporal, frequency,polarization or spatial diversity are successfully employed in theexisting wireless communication system.

[0003] Wideband CDMA (code division multiple access) types of systemsoccupy a bandwidth typically several times larger than the channel'scoherence bandwidth. Multi-path combining at the receiver turns thefrequency diversity of the channel into an inherent benefit of thesystem. However, indoor wireless channels have large coherencebandwidths and, therefore, usually offer no frequency diversity. Inorder to circumvent this coherent bandwidth problem, it is possible toassign the same copy of transmitted signal to different uncorrelatedtransmit antennas and spreading each of the assigned copies with adifferent delayed version of the same spreading code, wherein eachversion is offset by a few chips. This method, known as the CDMA DelayTransmit Diversity scheme, creates artificial multi-path propagation andtransforms a frequency non-selective channel into a frequency-selectivechannel.

[0004] Recent theoretical results in information theory have shown thatmultiple-input multiple-output (MIMO) wireless channels potentiallyoffer a linear increase in link capacity, providing that antennas at thetransmitter and receiver arrays are uncorrelated and that ubiquitous“key hold” effects do not occur in the channel. Multiple antenna systemswith the corresponding signal design (coding and modulation) are,therefore, seen as a key solution for high demand on transmission speedand reliability in future wireless systems. When the channel stateinformation (CSI) is not available at a transmitter, space-time coding(STC) is an optimal signaling strategy, designed to reach thetheoretical limits on MIMO Rayleigh fading channel capacity bysimultaneously coding across the spatial domain and the temporal domain.However, the complexity of the STC increases exponentially with thenumber of transmit antennas. In a theoretically optimal STC system, thecomplexity would reach the point when maximum likelihood decoding (MLD)becomes impractical or even unrealizable.

[0005] Lower complexity sub-optimal schemes based on the combining ofclassical single antenna channel coding with MIMO signal processing haverecently gained a huge interest. Current 3GPP standardization for highspeed down-link WCDMA FDD, as disclosed in “3^(rd) GenerationPartnership Project, Technical Specification Group Radio Access Network;Physical Layer Aspects of UTRA High Speed Downlink Packet Access” (3GTR25.848, v4.0.0 (2001-03)), is mainly concentrated around two proposalsfor multiple antenna transmission, VBLAST (Vertical Bell LabsSpace-Time) and the tradeoff between rate, puncturing and orthogonalityin space-time block codes for more than two transmit antennas.

[0006] VBLAST relies on spatial multiplexing at transmitter and spatialfiltering at receiver, to enable employment of single antenna channelcodes to MIMO systems. Detection is performed by successive nulling oflayers, which are not yet detected, combined with decision-directedinterference suppression of those layers previously detected. Spatialfiltering at receiver requires the number of receive antennas to begreater than or equal to the number of transmit antennas, which might beimpractical for down-link type of systems. Due to linear processing usedto suppress interfering signals, dominant diversity in this architectureis one. Applying powerful channel coding with iterative turbo detection(inter-antenna interference suppression) and decoding was alsoconsidered as a way to improve the performance, but the drawback of suchapproach is a further dramatic increase in receiver complexity.

[0007] A generalization of VBLAST, as introduced in Tarokh et al.“Combined Array Processing and Space-Time Coding” (IEEE Trans Inf. Th.vol. 45, no. May 4, 1999), proposes the application of lower complexitytwo antenna space-time trellis codes to more than two transmit antennas.Antennas at transmitter are partitioned into pairs, and individualspace-time trellis codes (STTC) (component codes) are used to transmitinformation from each pair of transmit antennas. More powerfulspace-time codes for two transmit antennas, i.e., space-time turbo codedmodulation (STTuCM) can be readily applied as component codes. At thereceiver, an individual space-time code is decoded with the help of aliner array processing (LAP) technique called, “the group interferencesuppression method”, that suppresses signals transmitted by other pairsof transmit antennas treating them as interference. The above methodenables the number of receive antennas to be reduced by half as comparedto VBLAST. Similar to VBLAST, the performance can be further improved byiterative, inter-antenna interference suppression and decoding with theprize of increased system complexity.

[0008] Single antenna channel codes and space-time codes applied toVBLAST and its generalization can be employed as a horizontally- orvertically-coded system with, the difference coming from position of theblock for serial-to-parallel conversion before or after the encodingblock, respectively. A horizontally-coded system will enable improveddecoded-based, decision-directed interference suppression, and thevertically-coded system is expected to benefit from averaged SNR(signal-to-noise ratio) over successive layers, i.e., spatialinterleaving.

[0009] Space-time block codes (STBC) were originally introduced as asimple transmit-diversity scheme (STTD) for power efficiency improvementby employing two antennas at the transmitter. STTD was later generalizedto an arbitrary number of transmit antennas, though the schemes for morethan two transmit antennas have a drawback of decreased rate as comparedto single transmit antenna systems. The main benefit of space-time blockcodes is a simple yet efficient exploitation of transmit antennadiversity, but even if some optimality is compromised for retrievedrate, the overall throughput is no higher than in single transmitantenna systems.

[0010] The spatial multiplexing of signals over different transmitantennas employed in VBLAST and its generalization assumed separation oftransmitted signals only at receiver. Being spreaded by the samespreading code and simultaneously transmitted over n different transmitantennas, signals arriving at the given receive antenna destructivelyinterfere each other. To detect the signal coming from the firsttransmit antenna, i.e., the first layer, n−1 interfering signals arenulled out by a linear ZF (zero-forcing) or MMSE (minimum mean squareerror) based spatial filtering method that requires a minimum of nantennas at the receiver. After the first layer has been detected, itscontribution to the received signals on different receive antennas issubtracted and detection of the next layer is performed in the samefashion. The above method increases the complexity of the mobile handsetin the downlink and has obvious limitations in the throughput determinedby the minimum required number of antennas in the receiver. Due to thelinear processing at the receiver, the dominant diversity in the systemis one.

[0011] It is advantageous and desirable to provide a method and systemfor spatial multiplexing of signals over different transmit antennaswherein the complexity can be reduced so that the method and system canbe used in a mobile handset.

SUMMARY OF THE INVENTION

[0012] It is a primary object of the present invention to reduce thecomplexity in spatial multiplexing of signals over different transmitantennas in a wireless communications system, wherein encoded data arespreaded prior to the modulation of encoded data for transmission. Thisobject can be achieved by interleaving and separating the encoded datainto data sub-streams prior to the spreading of the encoded data.

[0013] Thus, according to the first aspect of the present invention,there is provided a method (300) of processing information data (110) ina wireless communications system (1, 5) having a plurality of transmitantennas (22 ₁, . . . , 22 _(n)) for transmission, wherein the methodcomprises the steps of:

[0014] encoding (312) the information data for providing encoded data(112, 213);

[0015] spreading (318) the encoded data (112, 213) with a spreading code(180 ₀) for providing a first spreaded data stream (118 ₁, 218 ₁, 218₂);

[0016] spreading (318) the encoded data with at least one delayedversion (180 ₁, . . . , 180 _(n−1)) of the spreading code (180 ₀) forproviding at least one second spreaded data stream (118 ₂, 218 ₃, 218₄);

[0017] modulating (320) the first and second spreading-coded datastreams for providing modulated signals (120 ₁, . . . , 120 _(n), 220 ₁,. . . , 220 _(n)); and

[0018] conveying the modulated signals (120 ₁, . . . , 120 _(n), 220 ₁,. . . , 220 _(n)) to the transmit antennas (22 ₁, . . . 22 _(n)) fortransmission. The method is characterized by separating (316) theencoded data (112,213) into data sub-streams (116 ₁, . . . , 116 _(n),217 ₁, . . . , 217 _(n)) prior to said spreading (318), the datasub-streams including at least a first group of encoded data (116 ₁, 217₁, 217 ₂) and a second group of encoded data (116 ₂, 217 ₃, 217 ₄) suchthat the first spreaded data stream (118 ₁, 218 ₁, 218 ₂) is indicativeof the first group of encoded data (116 ₁, 217 ₁, 217 ₂) and said atleast one second spreaded data stream (118 ₂, 218 ₃, 218 ₄) isindicative of the second group of encoded data (116 ₂, 217 ₃, 217 ₄).

[0019] According to the present invention, the method is furthercharacterized by interleaving (314) the encoded data (112, 213) prior tosaid separating (316) such that the first group and second group ofencoded data (116 ₁, 217 ₁, 217 ₂) (116 ₂, 217 ₃, 217 ₄) are separatedaccording to said interleaving (314).

[0020] Advantageously, the encoded data (213) comprises a pair ofmutually orthogonal substream symbols (213 ₁, 213 ₂) and the method isfurther characterized in that

[0021] the data sub-streams (217 ₁, . . . , 217 _(n)) comprise at leasta first pairwise substream (217 ₁, 217 ₂) and a second pairwisesubstream (217 ₃, 217 ₄) of the substream symbol pair (213 ₁, 213 ₂),such that the first group of encoded data comprises the first pairwisesubstream (217 ₁, 217 ₂) and the second group of encoded data comprisesthe second pairwise substream (217 ₃, 217 ₄).

[0022] Advantageously, the encoded data (213) comprises a group of Nmutually orthogonal substream symbols (213 ₁, . . . , 213 _(N)), with Nbeing a positive integer greater than 2, and the method is furthercharacterized in that

[0023] the data sub-streams (217 ₁, . . . , 217 _(n)) comprise at leasta first group of N substreams and a second group of N substreams of thesubstream symbols, such that the first group of encoded data comprisesthe first group of N substreams (217 ₁, 217 ₂) and the second group ofencoded data comprises the second group of N substreams (217 ₃, 217 ₄).

[0024] According to the second aspect of the present invention, there isprovided a transmitter (1, 5) for processing information data (110) forproviding modulated signals (120 ₁, . . . , 120 _(n), 220 ₁, . . . , 220_(n)) for transmission via a plurality of transmit antennas (22 ₁, . . ., 22 _(n)), wherein the transmitter (1, 5) comprises:

[0025] means (12, 13), responsive to the information data (110), forproviding encoded data (112, 213);

[0026] means (18) for spreading the encoded data with a spreading code(180 ₀) for providing a first spreaded data stream (118 ₁, 218 ₁, 218₂), and for spreading the encoded data with at least one delayed version(180 ₁, . . . , 180 _(n−1)) of the spreading code (180 ₀) for providingat least one second spreaded data stream (118 ₂, 218 ₃, 218 ₄); and

[0027] means (20) for modulating the first and second spreaded datastreams for providing the modulated signals. The transmitter ischaracterized by

[0028] means (16, 17), responsive to the encoded data (112, 213), forseparating the encoded data into data sub-streams (116 ₁, . . . , 116_(n), 217 ₁, . . . , 217 ₂) prior to the spreading of the encoded databy the spreading means (18), the data sub-streams including at least afirst group of encoded data (116 ₁, 217 ₁, 217 ₂) and a second group ofencoded data (116 ₂, 217 ₃, 217 ₄) such that the first spreaded datastream (118 ₁, 218 ₁, 218 ₂) is indicative of the first group of encodeddata (116 ₁, 217 ₁, 217 ₂) and said at least one second spreaded datastream (118 ₂, 218 ₃, 218 ₄) is indicative of the second group ofencoded data (116 ₂, 217 ₃, 217 ₄).

[0029] According to the present invention, the transmitter is furthercharacterized by

[0030] means (14, 15), responsive to the encoded data (112, 213) forinterleaving the encoded data (112, 213) prior to the separation of theencoded data by the separating means (16, 17) such that the first groupand second group of encoded data (116 ₁, 217 ₁, 217 ₂) (116 ₂, 217 ₃,217 ₄) are separated according to said interleaving (314).

[0031] Advantageously, the encoded data (213) comprises a pair ofmutually orthogonal substream symbols (213 ₁, 213 ₂) and the transmitteris further characterized in that the data sub-streams (217 ₁, . . . ,217 _(n)) comprise at least a first pairwise substream (217 ₁, 217 ₂)and a second pairwise substream (217 ₃, 217 ₄) of the substream symbolpair (213 ₁, 213 ₂), such that the first group of encoded data comprisesthe first pairwise substream (217 ₁, 217 ₂) and the second group ofencoded data comprises the second pairwise substream (217 ₃, 217 ₄).

[0032] According to the third aspect of the present invention, there isprovided a wireless communications system (1, 3) (5, 7) comprising atransmitter (1, 5) and a receiver (3, 7), the transmitter (1, 5) havinga plurality of transmit antennas (22 ₁, . . . , 22 _(n)) fortransmitting modulated signals (120 ₁, . . . , 120 _(n), 220 ₁, . . . ,220 _(n)) indicative of information data (110) and the receiver (3, 7)having a plurality of receive antennas antennas (30 ₁, . . . 30 _(m))for receiving modulated signals, wherein the transmitter (1, 5)comprises:

[0033] means (12, 13), responsive to the information data (110), forproviding encoded data (112, 213);

[0034] means (18) for spreading the encoded data with a spreading code(180 ₀) for providing a first spreaded data stream (118 ₁, 218 ₁, 218₂), and for spreading the encoded data with at least one delayed version(180 ₁, . . . , 180 _(n−1)) of the spreading code (180 ₀) for providingat least one second spreaded data stream (118 ₂, 218 ₃, 218 ₄); and

[0035] means (20) for modulating the first and second spreaded datastreams for providing the modulated signals. The communications systemis characterized by

[0036] means (16, 17), responsive to the encoded data (112, 213), forseparating the encoded data into data sub-streams (116 ₁, . . . , 116_(n), 217 ₁, . . . , 217 _(n)) prior to the spreading of the encodeddata by the spreading means (18), the data sub-streams including atleast a first group of encoded data (116 ₁, 217 ₁, 217 ₂) and a secondgroup of encoded data (116 ₂, 217 ₃, 217 ₄) such that the first spreadeddata stream (118 ₁, 218 ₁, 218 ₂) is indicative of the first group ofencoded data (116 ₁, 217 ₁, 217 ₂) and said at least one second spreadeddata stream (118 ₂, 218 ₃, 218 ₄) is indicative of the second group ofencoded data (116 ₂, 217 ₃, 217 ₄).

[0037] According to the present invention, the communications system isfurther characterized in that

[0038] the transmitter (1, 5) further comprises means (14, 15),responsive to the encoded data (112, 213) for interleaving the encodeddata (112, 213) prior to the separation of the encoded data by theseparating means (16, 17) such that the first group and second group ofencoded data (116 ₁, 217 ₁, 217 ₂) (116 ₂, 217 ₃, 217 ₄) are separatedaccording to said interleaving (314).

[0039] Advantageously, the encoded data (213) comprises a pair ofmutually orthogonal substream symbols (213 ₁, 213 ₂) and thecommunications system is further characterized in that

[0040] the data sub-streams (217 ₁, . . . , 217 _(n)) comprise at leasta first pairwise substream (217 ₁, 217 ₂) and a second pairwisesubstream (217 ₃, 217 ₄) of the substream symbol pair (213 ₁, 213 ₂),such that the first group of encoded data comprises the first pairwisesubstreams (217 ₁, 217 ₂) and the second group of encoded data comprisesthe second pairwise substreams (217 ₃, 217 ₄).

[0041] The present invention will become apparent upon reading thedescription taken in conjunction with FIGS. 1 to 5.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a block diagram illustrating the transmitter, accordingto the OSM-1 method of the present invention.

[0043]FIG. 2 is a block diagram illustrating the receiver, according tothe OSM-1 method of the present invention.

[0044]FIG. 3 is a block diagram illustrating the transmitter, accordingto the OSM-2 method of the present invention.

[0045]FIG. 4 is a block diagram illustrating the receiver, according tothe OSM-2 method of the present invention.

[0046]FIG. 5 is a flowchart illustrating the method of processinginformation data for transmission, according to the present invention.

[0047]FIG. 6 is a chart showing the performance of the CC and TCVertically coded VBLAST method as compared to the corresponding OSM-1method, according to the present invention, wherein the comparison ismade with (4,4) system, single user case, 250 transmissions per layer,one and two equal power multipaths, quasi-static fading, un-correlatedantennas.

[0048]FIG. 7 is a chart showing the performance of the TC Verticallycoded VBLAST method as compared to the TC coded OSM-1 method, accordingto the present invention, wherein the comparison is made with singleuser and 50% load cases, 250 transmissions per layer, two equal powermultipaths, quasi-static fading, uncorrelated antennas.

[0049]FIG. 8 is a chart showing the performance of the STTC and STTuCMVertically coded LAP method as compared to the corresponding OSM-2method, according to the present invention, wherein the comparison ismade with single user case, 130 transmissions per layer, one and twoequal power multipaths, quasi-static fading, uncorrelated antennas.

[0050]FIG. 9 is a chart showing the performance of another STTuCMVertically coded LAP method as compared to the corresponding OSM-2method, according to the present invention, wherein the comparison ismade with single user and 50% load cases, 130 transmissions per layer,two equal power multipaths, quasi-static fading, uncorrelated antennas.

[0051]FIG. 10 is a chart showing the performance of Horizontally andVertically TC coded VBLAST, Horizontal and Vertically STTuCM coded LAP,and TC and STTuCM OSM-1 and OSM-2, wherein the comparison is made withsingle user, (4,4), two path equal power channel, quasi-static fading,uncorrelated antennas.

[0052]FIG. 11 is a chart showing the performance of VBLAST, LAP, OSM-1and OSM-2, wherein the comparison is made with 50% load, (4,4), two pathequal power channel, quasi-static fading, uncorrelated antennas.

BEST MODE TO CARRY OUT THE INVENTION

[0053] The present invention makes use of the good autocorrelationproperties of the spreading codes to separate or orthogonalize spatiallymultiplexed signals at the transmitter. Delayed versions of the samespreading code are applied to different individual or groups of transmitantennas, depending on the resolution of one or two for theorthogonalized spatial multiplexing (OSM) method. The method, accordingto the present invention, preserves the allocated number of spreadingcodes and enables a simple detection with just the use of matchedfiltering, i.e., RAKE receiver. Since the signals are separated alreadyat the transmitter, there are no restrictions in the terms of theminimum required number of receiver antennas. The diversity level of thesystem is equal to the number of employed receive antennas. As we willshow, the number of antennas at the receiver is determined by the levelof interference in the system and the desired system performance and istypically lower than in VBLAST.

[0054] Orthogonalized Spatial Multiplexing with the Resolution of One(OSM-1)

[0055] Block diagrams of a transmitter 1 and a receiver 3 for the OSMwith the resolution of one are depicted in FIG. 1 and FIG. 2,respectively. A transmitter 5 and a receiver 7 for the OSM with theresolution of two are depicted in FIG. 3 and FIG. 4, respectively. Asshown in FIG. 1, input information data 110 is encoded by a singleantenna channel encoder 12. Binary outputs 112 of the encoder 12 areinterleaved by an interleaver 14. The interleaved data stream 114 isconverted by the serial-to-parallel converter 16 into n parallelsubstreams 116 ₁, 116 ₂, . . . , 116 _(n). Each substream is spreaded bymeans of a mixer with a user specific spreading code 180 with asubstream-specific intentional delay offset D_(k) of few chips. Thedelayed versions of the spreading code are denoted by 180 ₀, 180 ₁, . .. , 180 _(n−1), wherein 180 _(k) is the spreading code delayed by adelay offset D_(k) and is used to spread the substream 116 _(k+1) bymeans of the mixer 18 _(k+1). After spreading, signals 118 ₁, 118 ₂, . .. , 118 _(n), from different substreams are modulated by modulators 20₁,. . . , 20 _(n). The modulated signals 120 ₁, . . . , 120 _(n) aretransmitted simultaneously over n transmit antennas 22 ₁, . . . , 22_(n).

[0056] As shown in FIG. 2, received signal 130 _(m) at each receiveantenna 30 _(m) is demodulated and de-spreaded by a module 32. Thereceived signal from each receive antenna is

[0057] indicative of all of the substreams 116 ₁, 116 ₂, . . . , 116_(n). Accordingly, a RAKE receiver (not shown) with n×L RAKE fingerssynchronized to the substream-specific, intentionally-introduced delaysD₁, . . . , D_(n−1) and the corresponding multipaths of the estimatedpower delay profile of the channel is used to process the receivedsignal from each receive antenna. L is the number of resolvablemulti-paths in the channel. As such, necessary detection statistics foreach substream are collected by maximum ratio combining (MRC) of RAKEfinger ouputs from different receive antennas and multipaths. Substreamsoft estimates 132 ₁, . . . , 132 _(n) are then converted by aparallel-to-serial converter 34. The combined signals 134 are thende-interleaved by a de-interleaver 36. The resulting data stream 136 isthen decoded by a channel decoder 38.

[0058] Orthogonalized Spatial Multiplexing with the Resolution of Two(OSM-2)

[0059] The OSM-1 scheme, as discussed in conjunction with FIGS. 1 and 2,can be generalized to OSM-2. As shown in FIG. 3, information data stream110 is first encoded by the space-time code (STC) encoder 13 for twotransmit antennas, which produces a pair of complex modulated substreamsymbols 213 ₁, 213 ₂. The STC can be either Space-Time Trellis Code(STTC), Space-Time Turbo Coded Modulation (STTuCM) or Space-Time BlockCode (STBC). Substream symbols 213 ₁, 213 ₂ are then interleavedpairwise on the symbol level by two interleavers 15 ₁, 15 ₂ andconverted with the pairwise serial-to-parallel converter 17 into n/2pairs of substreams (217 ₁, 217 ₂), (217 ₃, 217 ₄), . . . , (217 _(n−1),217 _(n)). Each pair of substreams is then spreaded via a mixer using auser specific spreading code 180 with a substream-pair, specificintentional delay offset D_(j) of few chips. The delayed versions of thespreading code are denoted by 180 ₀, 180 ₁, . . . , wherein 180 _(j) isthe spreading code delayed by an delay offset D_(j) and is used tospread the substream 271 _(2j+1) via the mixer 182 _(2j+1) and thesubstream 217 _(2j+2) via the mixer 18 _(2j+2). After spreading, signalpairs (218 ₁, 218 ₂), . . . (218 _(n−1), 218 _(n)) from differentsubstream pairs are modulated by modulators 20 ₁, . . . , 20 _(n). Themodulated signals 220 ₁, . . . , 220 _(n) are transmitted simultaneouslyover n transmit antennas 22 ₁, . . . , 22 ^(n).

[0060] As shown in FIG. 4, received signals 230 _(m) at each receiveantenna 30 _(m) are demodulated and de-spreaded by a module 33. Thereceived signal from each receive antenna is

[0061] indicative of all of the substream pairs (217 ₁, 217 ₂), . . . ,(217 _(n−1), 217 _(n)). Accordingly, a RAKE receiver (not shown) withn/2×L RAKE fingers synchronized to the substream-pair specificintentionally introduced delays D₁, . . . , D_(j), where j is equal to(n−2)/2, and the corresponding multipaths of the estimated power delayprofile of the channelis used to process the received signal from eachreceive antenna. Despreaded outputs from different receive antennas andmultipaths related to certain substream-pairs are then collected withoutany combining. Collected substream-pair soft outputs 233 ₁, 233 ₂, . . ., 233 _(n/2) are converted with a parallel-to-serial converter 35,deinterleaved by a de-interleaver 37, and passed to an STC decoder 39where, with the knowledge of the channel state information (CSI),combining is carried out within the decoder metric.

[0062]FIG. 5 summaries the orthogonalized spatial multiplexing method.As shown in the flowchart 300, input information data 110 is encoded atstep 312, depending on OSM-1 or OSM-2. According to the OSM-1 method,information data 110 is encoded into binary outputs 112 and interleavedat step 314 into an interleaved data stream 114. At step 316, theinterleaved data are separated into a plurality of parallel substreams116 ₁, . . . , each of which is spreaded with a delayed version of thesame spreading code 180 at step 318. After spreading, signals 118 ₁, . .. are modulated at step 320 into modulated signals 120 ₁, . . . fortransmission. According to the OSM-2 method, information data 110 isencoded into a pair of complexed modulated substream symbols 213 ₁, 213₂ and interleaved at step 314 into pairwise interleaved data streams 215₁, 215 ₂. At step 316, the pairwise interleaved data streams areseparated into a plurality of pairwise substreams (217 ₁, 217 ₂) . . . ,each of the pairs is spreaded with a delayed version of the samespreading code 180 at step 318. After spreading, signals 218 ₁, . . .are modulated at step 320 into modulated signals 220 ₁, . . . fortransmission.

[0063] Performance Comparison

[0064] The performance of the Convolutionally (CC) and Turbo (TC)vertically-coded VLBAST method has been compared to that of the OSM-1,according the present invention, for the single user case in single(L=1) and two (L=2) path equal power channel with four transmit and fourreceive antennas (4,4). For the case of two equal power multipaths(L=2), the slopes of the curves are the same, though TC coded OSM-1, ascompared to TC coded VBLAST, offers around 2.5 dB gain at FER of 10⁻¹,as shown in FIG. 6. In FIG. 7, the TC vertically-coded VBLAST and OSM-1are compared in the single user case and in the 50% loaded system. Inthe (4,4) case, OSM-1 strongly outperforms VLBAST, which in the 50%loaded case could not even reach the typically required FER for ARQ of10⁻¹.

[0065] The performance of a Vertically 32-state STTC and 2×8 stateSTTuCM-coded generalized BLAST (a linear array processing LAP) has beencompared to the performance of OSM-2 in single (L=1) and two (L=2) pathequal power channels in the (4,4) system, as shown in FIG. 8. STC-codedOSM-2 strongly outperforms vertically STC-coded LAP. When L=2 atFER=10⁻¹, STTuCM-coded OSM-2 outperforms STTC-coded OSM-2, VerticallySTTuCM-coded LAP and Vertically STTC-coded LAP by more than 1.5 dB, morethan 2.5 dB and around 4 dB, respectively. In FIG. 9, STTuCM-coded LAPand OSM-2 are compared in the single user and 50% loaded systems withL=2. In the multiuser case, the OSM-2 with (4,3) outperforms the LAPwith (4,4) by more than 1 dB at FER=10⁻¹. When both schemes use the samenumber of antennas (4,4) the performance gain of STTuCM-coded OSM-2, ascompared to Vertically STTuCM-coded LAP, is more than 8 dB.

[0066] The OSM-1 scheme is more pragmatic than OSM-2 in that OSM-1 canbe readily used with the existing 3GPP standardized codex (CC and TC).However, with the STTuCM with OSM-2 scheme, the performance of a WCDMAsystem can be farther dramatically improved.

[0067] In FIGS. 10 and 11, the performance of OSM-1 and OSM-2 aresummarized in the single user and 50% loaded case, respectively, with(4,4) and L=2. The performance of Horizontally TC-coded VBLAST andHorizontally STTuCM-coded LAP were also added for comparison. In FIG.10, the outage capacity of (4,4) channel with two equal power multipathswas also depicted. STTuCM coded OSM-2 outperforms all consideredschemes, performing within 1.5 dB away from 10% outage capacity. TCcoded OSM-1 outperforms both Vertically and Horizontally TC coded VBLASTin the both single user case and 50% loaded system.

[0068] The main advantages of the present invention are the significantperformance improvement and considerable complexity reduction ascompared to current 3GPP proposals. The combination ofserial-to-parallel conversion and the orthogonalized transmission fromdifferent uncorrelated transmit antennas act as a unique spatialinterleaving, which averages the SNR over the transmission layers. Thepowerful channel coding (TC and STTuCM) employed in conjunction with theOSM benefits from the spatial interleaving in the low mobilityapplications producing the large coding gains. Increasing the number oflayers, i.e., transmit antennas, the equivalent depth of the spatialinterleaving is increased, i.e., better SNR averaging is achieved.Therefore, along with the increased throughput, one would also expectbetter performance in terms of power efficiency as the number oftransmit antennas increases. However, increasing the number of transmitantennas increases the interference in the system, so the eventualperformance improvement in power efficiency is invested to compensatefor the increased interference at the receiver. However, the performanceresults show that good performance can be achieved with the simplematched filter based receiver and with the limited number of receiveantennas.

[0069] The number of receive antennas could possibly be furtherdecreased by investing some complexity in the more advanced receivers.

[0070] The present invention can be readily implemented to dramaticallyimprove the link level throughput and system capacity of the futureWCDMA multi-antenna wireless communication systems. It can be used fordownlink (base-to-mobile) communications, as future trends arepredicting two antennas in mobile handsets, which, in combination withthe polarization diversity, may provide an equivalent array with fourreceive antennas. The scheme can be readily implemented for lowconstraint delay services (voice transmission) as it has a superiorperformance already on extremely short frame sizes. In case of delaynon-constraint services (data transmission) larger frame sizes areusually used, which additionally improves the performance of the newscheme due to the implemented encoders. The combination with powercontrol over -different layers is one of the interesting topics forpossible further performance improvement.

[0071] In summary, the combination of serial-to-parallel conversion andthe orthogonalized transmission from different uncorrelated transmitantennas acts as a unique spatial interleaving which averages the SNRover the transmission layers. The powerful channel coding (TC andSTTuCM) employed in conjunction with the orthogonalized spatialmultiplexing benefits from the spatial interleaving in the lowermobility applications producing the large coding gains and highthroughputs. The method, according to the present invention, preservesthe allocated number of spreading codes and enables a simple detectionwith the use of matched filtering, i.e., RAKE receiver. Since thesignals are separated already at the transmitter, there are norestrictions in the terms of the minimum required number of receiverantennas. The diversity level of the system is equal to the number ofemployed receive antennas.

[0072] The present invention has been disclosed in conjunction withorthogonalized spatial multiplexing with the resolution of one (OSM-1)and with the resolution of two (OSM-2). It should be noted that thepresent invention can also be applied to orthogonalized spatialmultiplexing with the resolution of N (OSM-N), with N>2, by grouping Nantennas of the transmitter and applying different delayed versions ofthe spreading code to different groups of antennas. In a transmitterwith n antennas, there will be n/N of such groups. Similar to thetransmitter as shown in FIG. 3, the transmitter for OSM-N comprises anSTC encoder for encoding the information data stream into a group of Ncomplex modulated substream symbols 213 ₁, . . . , 213 _(N). Thesesubstream symbols are then interleaved by N interleavers and convertedby a serial-to-parallel converter into n/N groups of substreams forspreading.

[0073] Thus, although the invention has been described with respect to apreferred embodiment thereof, it will be understood by those skilled inthe art that the foregoing and various other changes, omissions anddeviations in the form and detail thereof may be made without departingfrom the scope of this invention.

What is claimed is:
 1. A method (300) of processing information data(110) in a wireless communications system (1, 5) having a plurality oftransmit antennas (22 ₁, . . . , 22 _(n)) for transmission, wherein themethod comprises the steps of: encoding (312) the information data forproviding encoded data (112, 213); spreading (318) the encoded data(112, 213) with a spreading code (180 ₀) for providing a first spreadeddata stream (118 ₁, 218 ₁, 218 ₂); spreading (318) the encoded data withat least one delayed version (180 ₁, . . . , 180 _(n−1)) of thespreading code (180 ₀) for providing at least one second spreaded datastream (118 ₂, 218 ₃, 218 ₄); modulating (320) the first and secondspreading-coded data streams for providing modulated signals (120 ₁, . .. , 120 _(n), 220 ₁, . . . , 220 _(n)); and conveying the modulatedsignals (120 ₁, . . . , 120 _(n), 220 ₁, . . . , 220 _(n)) to thetransmit antennas (22 ₁, . . . 22 _(n)) for transmission, said methodcharacterized by separating (316) the encoded data (112, 213) into datasub-streams (116 ₁, . . . , 116 _(n), 217 ₁, . . . , 217 _(n)) prior tosaid spreading (318), the data sub-streams including at least a firstgroup of encoded data (116 ₁, 217 ₁, 217 ₂) and a second group ofencoded data (116 ₂, 217 ₃, 217 ₄) such that the first spreaded datastream (118 ₁, 218 ₁, 218 ₂) is indicative of the first group of encodeddata (116 ₁, 217 ₁, 217 ₂) and said at least one second spreaded datastream (118 ₂, 218 ₃, 218 ₄) is indicative of the second group ofencoded data (116 ₂, 217 ₃, 217 ₄).
 2. The method of claim 1, furthercharacterized by interleaving (314) the encoded data (112, 213) prior tosaid separating (316) such that the first group and second group ofencoded data (116 ₁, 217 ₁, 217 ₂) (116 ₂, 217 ₃, 217 ₄) are separatedaccording to said interleaving (314).
 3. The method of claim 1, whereinthe encoded data (213) comprises a pair of mutually orthogonal substreamsymbols (213 ₁, 213 ₂), said method further characterized in that thedata sub-streams (217 ₁, . . . , 217 _(n)) comprise at least a firstpairwise substream (217 ₁, 217 ₂) and a second pairwise substream (217₃, 217 ₄) of the substream symbol pair (213 ₁, 213 ₂), such that thefirst group of encoded data comprises the first pairwise substreams (217₁, 217 ₂) and the second group of encoded data comprises the secondpairwise substreams (217 ₃, 217 ₄).
 4. The method of claim 1, whereinthe encoded data (213) comprises a group of N mutually orthogonalsubstream symbols (213 ₁, . . . , 213 _(N)), with N being a positiveinteger greater than 2, said method further characterized in that thedata substreams (217 ₁, . . . , 217 _(n)) comprise at least a firstgroup of N substreams and a second group of N susbstreams of thesubstream symbols, such that the first group of encoded data comprisesthe first group of N substreams and the second group of encoded datacomprises the second group of N substreams.
 5. A transmitter (1, 5) forprocessing information data (110) for providing modulated signals (120₁, . . . , 120 _(n), 220 ₁, . . . , 220 _(n)) for transmission via aplurality of transmit antennas (22 ₁, . . . , 22 _(n)), wherein thetransmitter (1, 5) comprises: means (12, 13), responsive to theinformation data (110), for providing encoded data (112, 213); means(18) for spreading the encoded data with a spreading code (180 ₀) forproviding a first spreaded data stream (118 ₁, 218 ₁, 218 ₂), and forspreading the encoded data with at least one delayed version (180 ₁, . .. , 180 _(n−1)) of the spreading code (180 ₀) for providing at least onesecond spreaded data stream (118 ₂, 218 ₃, 218 ₄); and means (20) formodulating the first and second spreaded data streams for providing themodulated signals, characterized by means (16, 17), responsive to theencoded data (112, 213), for separating the encoded data into datasub-streams (116 ₁, . . . , 116 _(n), 217 ₁, . . . , 217 _(n)) prior tothe spreading of the encoded data by the spreading means (18), the datasub-streams including at least a first group of encoded data (116 ₁, 217₁, 217 ₂) and a second group of encoded data (116 ₂, 217 ₃, 217 ₄) suchthat the first spreaded data stream (118 ₁, 218 ₁, 218 ₂) is indicativeof the first group of encoded data (116 ₁, 217 ₁, 217 ₂) and said atleast one second spreaded data stream (118 ₂, 218 ₃, 218 ₄) isindicative of the second group of encoded data (116 ₂, 217 ₃, 217 ₄). 6.The transmitter of claim 5, further characterized by means (14, 15),responsive to the encoded data (112, 213) for interleaving the encodeddata (112, 213) prior to the separation of the encoded data by theseparating means (16, 17) such that the first group and second group ofencoded data (116 ₁, 217 ₁, 217 ₂) (116 ₂, 217 ₃, 217 ₄) are separatedaccording to said interleaving (314).
 7. The transmitter (5) of claim 5,wherein the encoded data (213) comprises a pair of mutually orthogonalsubstream symbols (213 ₁, 213 ₂), said transmitter further characterizedin that the data substreams (217 ₁, . . . , 217 _(n)) comprise at leasta first pairwise substream (217 ₁, 217 ₂) and a second pairwisesubstream (217 ₃, 217 ₄) of the substream symbol pair (213 ₁, 213 ₂),such that the first group of encoded data comprises the first pairwisesubstreams (217 ₁, 217 ₂) and the second group of encoded data comprisesthe second pairwise substreams (217 ₃, 217 ₄).
 8. The transmitter ofclaim 5, wherein the encoded data comprises a group of N mutuallyorthogonal substream symbols (213 ₁, . . . , 213 _(N)), with N being apositive integer greater than 2, said transmitter further characterizedin that the data substreams (217 ₁, . . . , 217 _(n)) comprise at leasta first group of N substreams and a second group of N substreams of thesubstream symbols, such that the first group of encoded data comprisesthe first group of N substreams and the second group of encoded datacomprises the second group of N substreams.
 9. A wireless communicationssystem (1, 3) (5, 7) comprising a transmitter (1, 5) and a receiver (3,7), the transmitter (1, 5) having a plurality of transmit antennas (22₁, . . . , 22 _(n)) for transmitting modulated signals (120 ₁, . . . ,120 _(n), 220 ₁, . . . , 220 _(n)) indicative of information data (110)and the receiver (3, 7) having a plurality of receive antennas antennas(30 ₁, . . . 30 _(m)) for receiving modulated signals, wherein thetransmitter (1, 5) comprises: means (12, 13), responsive to theinformation data (110), for providing encoded data (112, 213); means(18) for spreading the encoded data with a spreading code (180 ₀) forproviding a first spreaded data stream (118 ₁, 218 ₁, 218 ₂), and forspreading the encoded data with at least one delayed version (180 ₁, . .. , 180 _(n−1)) of the spreading code (180 ₀) for providing at least onesecond spreaded data stream (118 ₂, 218 ₃, 218 ₄); and means (20) formodulating the first and second spreaded data streams for providing themodulated signals, characterized by means (16, 17), responsive to theencoded data (112, 213), for separating the encoded data into datasub-streams (116 ₁, . . . . 116 _(n), 217 ₁, . . . 217 _(n)) prior tothe spreading of the encoded data by the spreading means (18), the datasub-streams including at least a first group of encoded data (116 ₁, 217₁, 217 ₂) and a second group of encoded data (116 ₂, 217 ₃, 217 ₄) suchthat the first spreaded data stream (118 ₁, 218 ₁, 218 ₂) is indicativeof the first group of encoded data (116 ₁, 217 ₁, 217 ₂) and said atleast one second spreaded data stream (118 ₂, 218 ₃, 218 ₄) isindicative of the second group of encoded data (116 ₂, 217 ₃, 217 ₄).10. The system of claim 9, further characterized in that the transmitter(1, 5) further comprises means (14, 15), responsive to the encoded data(112, 213) for interleaving the encoded data (112, 213) prior to theseparation of the encoded data by the separating means (16, 17) suchthat the first group and second group of encoded data (116 ₁, 217 ₁, 217₂) (116 ₂, 217 ₃, 217 ₄) are separated according to said interleaving(314).
 11. The system (1, 3) of claim 9, wherein the encoded data (213)comprises a pair of mutually orthogonal substream symbols (213 ₁, 213₂), said system further characterized in that the data sub-streams (217₁, . . . , 217 _(n)) comprise at least a first pairwise substream (217₁, 217 ₂) and a second pairwise substream (217 ₃, 217 ₄) of thesubstream symbol pair (213 ₁, 213 ₂), such that the first group ofencoded data comprises the first pairwise substreams (217 ₁, 217 ₂) andthe second group of encoded data comprises the second pairwisesubstreams (217 ₃, 217 ₄).